A method of analyzing bubbly flow in a ball valve in a hydraulic circuit is presented. The dynamics of a single bubble can be well described by a quasi-static approximation of the Rayleigh-Plesset equation. Hence the presence of bubbles in low volume fractions can be modeled through an effective compressibility of the flow, which is easy to implement in commercial CFD packages. In the sample valve, a volume fraction of 4% air bubbles results in a mass flux reduction of up to 10%, as the bubbles expand due to the pressure drop in the valve and partly block it.